THE CAT 259 



Beginning with those of the hind legs, dissect out each of the 

 muscles that have been observed ; completely free it from the abut- 

 ting organs, remove all the fat and blood vessels, and find its 

 origin and insertion. Do not, however, disarticulate or injure any 

 of the bones. While studying the external oblique muscle note 

 that the abdominal wall is composed of the following muscles: 

 on the outside the external oblique ; just beneath it the internal 

 oblique, the fibers of which run at right angles to the fibers of 

 the external oblique ; the rectus abdominis, a long, narrow muscle 

 which, with its fellow, extends in the midventral area from the 

 pubis to the ribs and lies, anteriorly, between the aponeuroses of 

 the two obliques and, posteriorly, dorsal to both ; and, next to the 

 abdominal cavity, the transversus muscle, the fibers of which have 

 a transverse direction. 



The Skeletal System. This is made up of two portions, the 

 exoskeleton and the endoskeleton. The former consists of certain 

 special integumental structures : the hair, claws, and teeth. The 

 hairs are epidermal structures, which form a protective covering 

 against cold and external injuries. The whiskers, or vibrissae, are 

 enlarged hairs, the principal function of which is sensory. The 

 claws are horny epidermal structures allied to scales, each claw 

 consisting of a large dorsal scale, the unguis, and a minute ventral 

 scale, the subunguis, beneath its tip. The teeth have a twofold 

 origin: the dentine is a dermal structure, being modified dermal 

 bone, and the enamel an epidermal structure, arising as a secretion 

 of epidermal cells. 



The endoskeleton is the bony and cartilaginous framework of 

 the body. It may be divided into the axial skeleton, which in- 

 cludes the skull and the vertebral column, together with the ribs 

 and the sternum, and the appendicular skeleton, which includes 

 the framework of the extremities.- 



To prepare the internal skeleton for study, open the abdominal 

 cavity, without injuring the sternum or ribs, and remove all the 

 viscera. Cut away the diaphragm and remove the heart and 

 lungs and other thoracic organs. Remove the greater part of the 

 muscles which still remain in the body, being very careful not to 

 injure the bones. 



